1. Field of the Invention
The present invention relates generally to timing circuitry and, more particularly, but not by way of limitation, to circuitry for providing a timed disengagement of an electrically actuated transmission brake of a racing automobile in response to release of a starting switch by the driver of the automobile.
2. Discussion of the Prior Art
The difference between winning and losing a drag race is often measured in thousandth's of a second with the result that getting off to a good start in a race has become a mater of great importance to race car drivers. Because of this, drivers of drag racing cars generally do not wait until they are given a green light on the so-called "Christmas Tree" that controls the starting of a race to take action that will launch their automobiles down the race track. Instead, they utilize other lights that come on before the green light to initiate a chain of events that ends in the disengagement of an electrically actuated transmission brake with which their automobiles are equipped at the moment that or, preferably, slightly before, the green light comes on.
The lights on the "Christmas Tree" are used not only to time the start of a race but also to insure that the racing cars in proper position at the beginning of a race. For the latter purpose, each of two tracks is provided with sensors, light beams and photocells, that define the proper position for the front wheels of participating automobiles at the start of the race. Circuitry connected to these sensors then indicate to the drivers when they are in proper position. Thus, before the race begins, each automobile in the race is inched forward, by momentary disengagements of the transmission brake, until its front wheels cut a first light beam that causes a prestaging light on the "Christmas Tree" to go on and then again inched forward until a second light beam, causing a staging light to be turned in, is cut. When both the prestaging and staging lights are on for both automobiles in a race, the race is ready to begin.
In addition to the green light, the prestaging light and the staging light, the "Christmas Tree" has a red light that is controlled by the light beam and photocell that actuates the prestaging light and the red light is used to prevent a racer from jumping the gun. If he moves out of position before the green light comes on, so that the prestaging light photocell becomes illuminated, the red light comes on and he loses the race by default. Thus, the ideal start is one in which the transmission brake is disengaged at a time that will cause the racing automobile to be in motion when the green light comes on but in a position in which the automobile will not have moved a distance from the starting position sufficient to result in a red light. Additional lights, often three in number, are provided on the "Christmas Tree" to enable the race car driver to try for this ideal start.
The additional lights are arranged in a vertical row above the green light and come on at half second intervals with the last of them coming on a half second before the green light comes on. Thus, the drivers of drag racing automobiles are in a position to judge the time the green light will come on and react accordingly. This judgement was replaced a few years ago when a timing circuit that eliminated the need to estimate the time the green light will come on was developed. Instead, the circuit was used to disengage the transmission brake and it included a programmable down counter and clock that began a timing sequence when a starting switch was released. Thus, the driver could release the starting switch when the first of the series of lights above the green light came on and the transmission brake would be disengaged when the counter reached a zero count. Since a driver could allow for his reaction time in setting the counter, the introduction of this circuit, which is now in widespread use, theoretically placed him in a position to attain an ideal start.
In practice, the ideal has not been achieved prior to the present invention. It will sometimes occur that the driver of a racing automobile will be distracted by other events when the starting series begins so that he misses the first light in the series. Since the prior art circuit is constructed to disengage the transmission brake at a fixed time following the release of the starting switich, the result is that he gets off to a late start and loses the race. Moreover, the prior art circuit does not permit the driver of a racing automobile to exercise his judgment if he senses that he has mistimed his release of the starting switch. Once the switch is released in the prior art circuit, the chain of events leading to the disengagement of the transmission brake cannot be reversed without starting anew and missing the green light.
Additionally, a danger exists with this circuit that can lead not only to the loss of a race but also to damage to the racing automobile. The circuit is used in an environment characterized by vibration and heat which can give rise to spurious signals that can have the effect of turning on electronic components of the circuit. Thus, it is possible for the circuit to engage the transmission brake during a race and such engagement of the transmission brake can severely damage the transmission of the racing automobile. The transmission brake operates, in effect, by placing the automobile in both forward and reverse gear at the same time so that the transmission becomes locked up in trying to cause mutually exclusive motions of the automobile. So long as the wheels of the automobile are not turning, such locking of the transmission will cause no harm. However, if the automobile is moving when the transmission brake engages, the transmission brake must work against the motion of the wheels, to bring them to a sudden stop, with the result that the transmission is subjected to large reaction forces that are capable of doing severe damage to the transmission.